The present invention relates to a pre-combustion chamber for use with an internal combustion engine. In particular, the present invention relates to a pre-combustion chamber assembly for use in conjunction with a conventional spark plug in the cylinder head of an internal combustion engine.
Pre-combustion chambers are known in the art and have been applied to provide an ignition system for internal combustion engines. Pre-combustion chambers have found particular application in internal combustion engines operating on gaseous fuels, such as natural gas. The engine is commonly supplied with a lean fuel mixture, that is a mixture of air and fuel containing a relatively high ratio of air to fuel. The lean fuel mixture often results in misfires, detonation, incomplete combustion and poor fuel economy. These characteristics have been traced to the poor ability of conventional spark plugs to effectively ignite a lean fuel mixture in the cylinder of the operating engine. More effective conbustion of lean fuel mixtures can be achieved using a precombustion chamber.
In the past, the incorporation of a pre-combustion chamber into an existing internal combustion engine has required substantial modification to the cylinder head of the engine. It will be readily understood that such a modification requires a significant time to effect, during which the engine will typically be inoperative. In addition, such a modification requires extensive machining and fabrication facilities, in turn preventing the modification from being one capable of being carried out in the field at the site or location of the engine.
In view of these problems, it has been proposed to provide a pre-combustion chamber assembly for converting existing, conventionally ignited engines. Thus, U.S. Pat. No. 5,431,140 discloses a pre-combustion chamber system for installation on an internal combustion engine using the existing spark plug hole in the cylinder head. The pre-combustion chamber system comprises a pre-combustion chamber, around which extends a jacket for containing a supply of coolant, such as cooling water. The pre-combustion chamber system comprises an inlet and an outlet for the coolant. The pre-combustion chamber is further provided with a threaded hole, into which a spark plug may be inserted and secured and an inlet for fuel. In use, the pre-combustion chamber is inserted into a spark plug well of the engine and threaded into the pre-existing threaded hole for the spark plug in the cylinder head of the engine. A port extends from the pre-combustion chamber and communicates with the main combustion chamber of the respective cylinder of the engine. In operation, fuel is fed to the pre-combustion chamber and is ignited at the appropriate time in the cycle of the engine by the spark plug. A stream of combusting gas flows from the pre-combustion chamber, through the port and into the main combustion chamber of the cylinder, where the main charge of fuel and air is ignited, providing the power stroke of the engine.
While the device of U.S. Pat. No. 5,431,140 proved effective in use, problems arose, leading to an undesirably short operating life span of the device. In particular, it was found that the assembly suffered from stress cracking and accelerated fatiguing. It was found that this was due to differential expansion occurring between the walls of the pre-combustion chamber and the outer wall of the coolant jacket. In use, the inner wall of the pre-combustion chamber is exposed to considerable heat, in turn causing the wall to expand. In contrast, the outer wall of the coolant jacket remains at the temperature of the coolant, which is substantially lower than that of the pre-combustion chamber wall. This difference in temperature leads to a difference in the rate and amount of thermal expansion undergone by the two aforementioned walls, in turn leading to stress cracking and failure of the device.
To overcome this problem, U.S. Pat. No. 5,662,082 proposed a modified pre-combustion chamber system. In the modified system, an inner wall defines the pre-combustion chamber and an outer wall extending around the inner wall provides for a coolant jacket, as in the earlier device. However, in the device of U.S. Pat. No. 5,662,082, the outer wall is secured at one end to the inner wall, while the second end is free to float with respect to the inner wall. In this way, movement of the inner wall with respect to the outer wall, for example due to differential thermal expansion, may be accommodated without inducing stress cracking in either component. A seal is placed between the inner and outer wall in order to close the cooling jacket and prevent escape of the coolant liquid. In a preferred embodiment, redundant seals are employed in order to ensure that coolant leakage is prevented.
In use, it has been found that the device of the general design of U.S. Pat. No. 5,662,082 is effective in extending the working life of the pre-combustion chamber device. However, it has also been found that, although increased, the working life of the device remains undesirably short. In particular, it has been observed that the devices fail as a result of excessive heat build up within the device.
Accordingly, there is a need for an improved pre-combustion chamber device, which may be fitted in the spark plug well of an existing engine, and which has a prolonged operating lifetime.
According the present invention there is provided a pre-combustion chamber assembly for an internal combustion engine, the pre-combustion chamber assembly comprising:
an inner housing defining a pre-combustion chamber, the housing having a receiver for receiving a spark plug and an inlet for fuel;
a connector for securing the pre-combustion chamber in a spark plug well of the internal combustion engine, the connector comprising a port for connecting the pre-combustion chamber with a combustion chamber of the internal combustion engine;
an outer housing having a first end and a second end and extending around the inner housing; and
a chamber defined between the inner and outer housings; wherein
the outer housing being releasably retained around the inner housing so as to allow relative movement between portions of the inner and outer housings while maintaining the integrity of the chamber.
It has been found that the operational life of the pre-combustion chamber assembly can be significantly improved by having the outer housing releasably retained around the inner housing, so as to allow relative movement between the inner and outer housings. In this way, relative movement between the two housings, as a result of expansion of the inner housing relative to the outer housing, can be accommodated. However, an investigation into the pre-combustion chambers has shown that simply providing for relative movement between the two housings is insufficient to effectively prolong the operational life of the assembly. It has been found that a build up of deposits and scale occurs within the chamber, reducing the heat transfer capabilities of the assembly. This has been found to occur as a result of cooling water remaining in the chamber after the engine has been shut down being caused to boil and evaporate as a result of heat remaining in the pre-combustion chamber assembly. This evaporation causes a rapid build up of scale to occur within the chamber. The heat transfer of the scale is such that it reduces the ability of the cooling medium in the chamber to remove heat from the pre-combustion chamber. This in turn has been found to lead to the pre-combustion chamber operating at ever increasing temperatures, leading to the eventual failure of the pre-combustion chamber assembly.
By having the outer housing releasable, it is now possible to clean both the outer wall of the inner housing and the outer housing as part of a maintenance program, thereby restoring the cooling capabilities of the chamber and the cooling medium within it. This has not proven possible with the pre-combustion chamber assemblies of the prior art, without embarking upon a major disassembly of the assembly, including cutting portions of the housing away. Replacement of the housing involves welding and stress relieving, before the assembly can be returned to operation. As will be appreciated, such a maintenance schedule is very costly and time consuming. This has led to the practice of simply discarding the used assemblies and replacing them with new ones.
The outer housing is preferably free to move both axially and circumferentially with respect to the inner housing.
In a first embodiment, the outer housing is fixed to the inner housing at its first end. The inner housing is free to move with respect to the outer housing at the second end of the outer housing. The outer housing may be secured to the inner housing at its first end by any suitable means known in the art, for example a simple threaded connection. In a preferred embodiment, the outer housing is retained around the inner housing in such a way that the inner housing is free to move with respect to the outer housing at both the first and second ends of the outer housing.
The outer housing may be retained around the inner housing by a retainer acting against the first end of the outer housing. The retainer is preferably a retaining ring seated in a groove in the inner housing at the first end of the outer housing. In operation, a cooling medium, such as water, is introduced into the chamber between the inner and outer housings. Metal to metal contact between the inner housing and the outer housing may suffice to retain the cooling medium within the chamber. Preferably, however, a seal is provided between the first end of the outer housing and the inner housing.
A further retainer may be provided to retain the outer housing at its second end. The further retainer may be any suitable retaining means, such as a retaining ring seated in a circumferential groove in the inner housing at the second end of the outer housing. However, it is convenient to form the inner housing with a shoulder, against which the second end of the outer housing can be brought to bear when the outer housing is first installed around the inner housing. In use, expansion of the inner housing will cause the shoulder to move away from the second end of the outer housing. Contact between the outer housing and the inner housing at the second end of the outer housing may be sufficient to retain the cooling medium with the chamber. Preferably, a seal is provided between the second end of the outer housing and the inner housing.
The connector for securing the pre-combustion chamber assembly in the spark plug well of the internal combustion engine has a first end adjacent the pre-combustion chamber and a second end, which, when the assembly is installed, extends into the bore in the cylinder head for the spark plug. In preferred embodiment, the port through the connector is arranged to generate a turbulent or swirling flow pattern for the hot gases leaving the pre-combustion chamber and entering the combustion chamber of the engine during operation. To achieve this, the port has a first opening in the first end of the connector within the pre-combustion chamber and a second opening in the second end of the connector. The first opening is offset from the central longitudinal axis of the pre-combustion chamber. Preferably, the second opening is offset from both the first opening and the central longitudinal axis of the pre-combustion chamber. In a preferred arrangement, the offset of the second opening from the central longitudinal axis of the pre-combustion chamber is greater than that of the first opening.
In a further aspect, the present invention provides an internal combustion engine comprising at least one cylinder having a combustion chamber, the engine further comprising at least one cylinder head assembly, the cylinder head assembly comprising a spark plug well and a threaded bore extending into the combustion chamber, the engine further comprising a pre-combustion chamber assembly in the spark plug well, the pre-combustion chamber assembly comprising:
an inner housing defining a pre-combustion chamber, the housing having a receiver for receiving a spark plug and an inlet for fuel;
a connector threaded into the threaded bore for securing the pre-combustion chamber in the spark plug well, the connector comprising a port for connecting the pre-combustion chamber with the combustion chamber;
an outer housing having a first end and a second end and extending around the inner housing; and
a chamber defined between the inner and outer housings; wherein
the outer housing being releasably retained around the inner housing so as to allow relative movement between portions of the inner and outer housings while maintaining the integrity of the chamber.
The features of the pre-combustion chamber assembly of the internal combustion engine are as hereinbefore described.
In still a further aspect of the present invention, there is provided a method of modifying an internal combustion engine, the method comprising securing in a spark plug well of the engine a pre-combustion chamber assembly, the pre-combustion chamber assembly comprising:
an inner housing defining a pre-combustion chamber, the housing having a receiver for receiving a spark plug and an inlet for fuel;
a connector for securing the pre-combustion chamber in the spark plug well of the internal combustion engine, the connector comprising a port for connecting the pre-combustion chamber with a combustion chamber of the internal combustion engine;
an outer housing having a first end and a second end and extending around the inner housing; and
a chamber defined between the inner and outer housings; wherein
the outer housing being releasably retained around the inner housing so as to allow relative movement between portions of the inner and outer housings while maintaining the integrity of the chamber.
Specific embodiments of the apparatus and method of the present invention will now be described in detail having reference to the accompanying drawings. The detailed description of these embodiments and the referenced drawings are by way of example only and are not intended to limit the scope of the present invention.